How many miles is the bottom end good for before a rebuild is required? I’m planning a Vortec head swap on my 78 L-82 and it has 60,000 miles on it. I’m having no oil loss or burning problems, normal oil pressure and I have good compression on all cylinders. But I was wondering if it made since to pull the motor, freshen up the bearings and rings while I was this far into it?

 

I'm not sure there is any kind of definite answer to a question like that - too many variables such as how easy or hard was the motor used during those 60,000 miles, how good was the maintenance during that time, etc.
Why not wait until the motor is opened up than evaluate the bottom end than while it can be inspected than plan your rebuild accordingly.
The L82 bottom end should be fine after only 60,000 miles assuming the motor wasn't beat to death and it was maintained well but you never know.

 

any answer would be a vast generalization..for example my L-82 at 104k didnt show any perceptible ridge at the top of the cylinder bore, still made excellent oil pressure and maintained good cylinder pressure...while i dont know how the motor was treated by previous owners mine wasnt raced and was maintained like any old car motor should.

at 104k it wiped a lobe on the original cam - rebuild was basicly stab a new cam.

Alternately I've seen motors that at 60k were complete and utter basket cases..

If a rebuild is in the cards for you, take the short apart and inspect it..in all likelyhood it could be reused as is..it may last another 60 or so. I at the very least would re-ring and bearing any rebuild of a motor that had 60k miles on it before the build...simply for cheap insurance.

 

Guys are right on here. Once you get it opened up, base your decision on things like how much ridge there is in the cylinders, and just the general appearance of the lower end.

BUT, you're going to have it out, it's no big step from there to do rings and bearings. Assuming all the crank/rod/cylinder bore measurements are within tolerances, and you add a couple of things to the parts list, (oil pump/pickup) you KNOW what you have for sure. No guesswork. And if you get the block hot tank cleaned, it'll be just like new. (and the paint will stick!)

 

At 60K you would be wasting your time unless the motor was left underwater or somehow sand got in the oil past the filter. The taxi cabs ran the sb chevy and have a good data base for overhaul - 350K mi. Yes 350,000 mi. Now if the car has sat alot then maybe the seals dried out and may need replacement - just timing cover over the snout and the rear main which will require u to drop the oil pan (a great time to take a look inside too). And the nice part is you can drop the oil pan on a corvette with engine and trans in car.
But really all the bearings are covered well (nearly sealed) by the bearing caps and long term storage is not a problem for brgs - this is from what i have seen myself on mine. Usually just the seals will dry out without periodic use. But u can replace seals at your own choice.
A leakdown test for your own info would be nice before removing heads. This would give you an idea of the cylinders condition. Save yourself a lot of work and just do the head swap first.: :

Just to help you here if you have never taken an engine apart before - even just the heads - make sure u know how to tune the ignition and carb first. I just read too many horror stories right here were new C3 owners ruin an entire overhaul because the new engine won't start. Yes first priority is to setup your timing - not just the initial but the entire timing curve including changing dist weights and springs. Next set the carb mixture - not just the idle mix screws but the mix rods on Qjet or jets on Holleys. This is a lot more headwork and research than labor but very little $$$ to tune the engine. And u will be surprised how much HP is from just a good tune.

Hope this helps ya',
cardo0

 

Very good info. I’m dropping the oil pan anyway to replace the rear seal and remove the timing chain cover for a cam swap. I will check the rear main and one rod bearing while I’m down there. Do you guys have pics of what a ‘worn’ bearing looks like? I have checked the compression and I’m in good shape but while I have the heads off, I’ll check the cylinders for scratches and ridges.
Thanks Cardo0 for the heads-up on the tuning, I understand the importance of the engine starting immediately after a cam swap. I’m also very familiar with both of Lars ignition and Quadrajet tuning papers.
Thanks for the guidance..

 

60k Id go for it. If you have to pull bearings youll know by looking at them .either deep scores or copper showing everywhere.

 

I don't have pix but u may see some shadow discolor on the brgs where the crank lays once stopped w/o oil press - don't worry over a little discolor just the deep wear.
It was good to read u realize the importance of good tune as the '78 cars were significantly detuned in timing and mixture for smog - something like at least 30hp. A lot of new C3 owners put too much effort and $$$ into hp parts that never seem to produce as expected because the eng remains out of tune with the old dizzy and carb settings.

One more thing the L-82 had a decent preformance cam (much better than the L-48 and I think the L-82 cam is still used the Chevy crate mtrs). Now with 60K it would be a good time to replace the cam as cams have a much shorter life than the bottom end (as the full lift wears out). But that L-82 cam (#3896962 or HO cam #24502476 i think) is a great match for those Vortec heads with the increase in compression they give. And u can buy that cam as a repro for fairly cheap through most parts houses - and u know it will drive great around town with good power.

Happy tuning and good luck,
cardo0

 

You are right, the L-82 is an excellent cam for this setup. The cam choice was one of the first things I tackled when I started this. Billla provided me some good feedback and DD'd some cam combinations for me. The L-82 cam was in the short list.
http://forums.corvetteforum.com/show...2118109&page=2

I decided to go with the Lunati Bracket Master
http://www.lunaticams.com/Product.aspx?id=2416&gid=292

Thanks again for feedback.

 

Check everything first.
Check cam lobe lift ... if you want L82 cam ... and have old L82 ... and the L82 cam&lifters you have is not worn ... you're better off reusing L82 cam&lifters you have 'cuz it's already bedded in ... most flattappet cam&lifter failures occur during or soon after breakin.

 

A compression check would yield some good data to start with...

 

Normally i would recommend just swapping the heads and use the stock cam again but back in the 70's GM used a lot of nylon timing gears that died somewhere after 50k mi - so a new timing set is a good idea here and that begs for cam upgrade too. Now the #24502476 HO cam is a better match for a car using the original ram horn exh manifolds because of the extra exh duration and tighter lobe separation. Extra duration on the exh will help more with the more restricted stock exh. The tighter lobe separation will make more torque in the mid range that the stock L-82 cam. But the Luanti 290/290 cam will just have too much overlap - a single pattern cam would breath better through headers. A critical note here is that Chevys adv duration numbers are kinda non-sensible when u look at them (320*/324*) and here is a case where u may use the 0.050" to 0.050" duration value for comparison. Don't compare GM's adv duration numbers to Lunati's - not even similar.
As for the L-82 cam #3896962 it is single pattern cam too with a wider LSA (BTW take a look at it's adv duration too = 312*/312* just for comparison). What i want to say is that HO 2476 cam will make even more mid range torque than the Bracket Master II and drive a heck of a lot better on the street with enough vacuum for your accessories. What the DD doesn't tell you is things like vac for pwr brakes and headlights. Neither does the dynamic compression ratio miscalculator.

Just trying to help and i know now u will listen so good luck with what ever u choose,
cardo0

 

I’m certainly no expert on this stuff; just enjoy drinking beer and turning wrenches. Opinions and experience is what I like about these forums. Here’s my cam short list. I agree, the Lunati cam is probably on the edge of being too big. The GM 24502476 or Crane Blue Racer is probably a safer choice. The XE262 pushes the lift limit on the stock Vortecs.

Here’s a link I stumbled across a few days ago that has some good discussion on the GM cams and Vortec heads.
http://www.chevelles.com/forums/arch.../t-111053.html

*Cam List*
Summit SUM-K1103
Intake Lift-0.442
Exhaust lift-0.465
Intake duration @ .050"-214
Exhaust duration @ .050"-224
Lobe Centerline- 112

GM 24502476
Intake Lift-0.435
Exhaust lift-0.460
Intake duration @ .050"-212
Exhaust duration @ .050"-222
Lobe Centerline- 112

Crane WG1159K
Intake Lift-0.442
Exhaust lift-0.465
Intake duration @ .050"-214
Exhaust duration @ .050"-222
Lobe Centerline- 112

GM 3896962
Intake Lift-0.450
Exhaust lift-0.460
Intake duration @ .050"-222
Exhaust duration @ .050"-222
Lobe Centerline- 114

Recommendations from Vendors
Lunati 00017
Intake Lift-0.460
Exhaust lift-0.460
Intake duration @ .050"-224
Exhaust duration @ .050"-224
Lobe Centerline- 112

Crane 113512
Intake Lift-0.446
Exhaust lift-0.459
Intake duration @ .050"-212
Exhaust duration @ .050"-218
Lobe Centerline- 114

Comp XE262H
Intake Lift-0.462
Exhaust lift-0.469
Intake duration @ .050"-218
Exhaust duration @ .050"-224
Lobe Centerline- 110

 

just pulling the heads isnt "getting that far into it".Whole lotta less work,as the engine remains nestled in the car. As the exhaust manifolds must be disconnected,this might be a good time to consider header installation. If you do pull it,by all means,replace mains/rod bearing/rings/timming gear/chain/oil pump.. Question is,why strip it that far down without going one step futher? get the clyinders honed and new cam bearing installed. Its ver easy to get carried away in a project like this...jut change the heads for now,and mabe throw on some headersThe car will be down for only one day that way.

 

Getting carried away is easy My intent all along was to replace the ole stock heads, cam/lifters and convert to true duel exhaust. Since I'm replacing the cam, the timing chain and gear will also get replaced. The oil pump is only 5 years old so it should be OK. On the headers note, my original intent was to stick with the stock manifolds and get the duel kit from Mid America. However, I have since realized for the same money I can get a set of Jegs headers and Hooker header back duel kit. I have been reluctant to make the move to headers because of heat and leak problems Ive heard from other forum members. But your right, If I'm this far into it, headers may make since now. I have some time to think about this stuff because I don't plan to start anything till mid Nov.

 

I'll respectfully disagree. These measurements will virtually never be within tolerances - so a decision to tear down the bottom end will be a decision to do an overhaul.